1. Field of the Invention
This invention relates to an asymmetric polymer and to a composition of matter comprising the same. More particularly, this invention relates to an asymmetric polymer which will alter the viscoelastic properties of a composition of matter comprising the same and to a composition of matter comprising the same.
2. Prior Art
Methods for varying the elasticity of polymers are, of course, well known in the prior art and such methods are taught in U.S. Pat. No. 4,620,048. The invention described in U.S. Pat. No. 4,620,048 has been described by reference to polymeric viscosity index (V.I.) improver additives and patentees clearly indicate that the parameters which affect elasticity of the polymer will interact to affect the viscoelastic properties of a composition containing the polymer. One such parameter is molecular topology. The thrust of the invention described in U.S. Pat. No. 4,620,048 seems to be that mechanical degradation of the polymer may be reduced if the compliance of the polymer is reduced or if the molecular weight of the polymer is narrowed. There is, apparently, no indication in U.S. Pat. No. 4,620,048 that the performance of such a polymer might show even further improvement as a V.I. improver as a result of the improved elastic property, per se, at least in certain cases as when used in a lubricating composition lubricating journal bearings. The thrust of the present invention, then, resides in this latter discovery with the polymer of this invention.
It is well known in the prior art that a reduction in HTHSR viscosity will improve fuel efficiency. This is taught for example in ASTM Data Series Publication, DS62 "The Relationship Between High Temperature Oil Rheology and Engine Operation" published in 1984 and confirmed in the paper by D. C. Olson, SAE Paper, 87128. A mere reduction in HTHSR viscosity will, however, genereally result in an increase in journal bearing wear in an automotive engine.
More recently, it has been established that bearing oil film thickness, which affects bearing wear, is proportionate to both the HTHSR viscosity and the oil elasticity. This is taught in SAE Paper 860376, by Bates et al. This discovery too is confirmed by the aforementioned Olson Paper. It follows from this discovery that improved journal bearing wear could be realized if the oil elasticity could be increased while maintaining the same HTHSR viscosity and improved fuel efficiency could be realized and journal bearing wear maintained with a lower HTHSR viscosity by increasing the oil elasticity. The aforementioned U.S. Pat. No. 4,620,048 does teach that oil viscoelastic properties of an oil can be changed by changing the topology of the polymer added to the oil as can the shear stability of the oil composition. There is, however, no teaching or suggestion in this patent that both fuel efficiency and bearing wear can be improved if the proper topology is selected.
In light of the foregoing, a need remains for a polymer which can be added to an oil and improve the oil fuel efficiency while maintaining or improving journal bearing wear properties.